Heat-sealing sheet material

Abstract

A heat-sealing sheet material can be obtained by forming, on one side of a sheet base material such as aluminum foil, a sealant layer composed of a graft copolymer comprising a trunk polymer of a 20 to 60% saponification product of an ethylene/vinyl acetate copolymer having a vinyl acetate content of 15 to 45% by weight and a branch polymer of an unsaturated carboxylic acid in a proportion of 10% by weight or less of the partially-saponified product. This sheet material exhibits excellent heat-sealing strength with respect to glass containers, and, moreover, there is almost no decrease in the sealing strength even when the material has been in contact with water. Accordingly, the sheet material is suitable as a sealing material for the opening rims of glass containers for water-containing food products such as jams and pickles.

What is claimed is: 
     
       1. A heat-sealing sheet material which comprises a base sheet and a sealant layer formed on one side of the base sheet, said sealant being a graft copolymer comprising a trunk polymer of a 20 to 60% saponification product of an ethylene/vinyl acetate copolymer (EVA) of a vinyl acetate content of 15 to 45% by weight and a branch polymer of an unsaturated carboxylic acid in a proportion of 10% by weight or less of the graft-copolymer. 
     
     
       2. A heat-sealing sheet material according to claim 1 wherein the base sheet comprises a metal foil. 
     
     
       3. A heat-sealing sheet material according to claim 1 wherein the base sheet comprises a laminate of an aluminum foil and a polyethylene film, and the sealant layer is formed on the polyethylene film. 
     
     
       4. A heat-sealing sheet material according to claim 1 wherein the base sheet has a thickness of 20 to 100μ. 
     
     
       5. A heat-sealing sheet material according to claim 1 wherein the sealant layer has a thickness of 10 to 100μ. 
     
     
       6. A heat-sealing sheet material according to claim 1 wherein the unsaturated carboxylic acid is maleic acid. 
     
     
       7. A sealed glass container which comprises a glass container containing a product and having an opening rim and a heat-sealing sheet material of claim 1 affixed on the opening rim of said container with the sealant layer in heat-sealed contact with the opening rim. 
     
     
       8. A sealed glass container according to claim 7 wherein the product is a water-containing food product.